I have a friend who thinks that religion is just a way for the government to keep the people down. I know a student who claimed to love Jesus but then changed to an athiest. I know people who say that they know the God I know, but choose to not follow Him. I know people that are wondering around looking for something to fill them up, but they never find 'it'. I know people who say "how do you know?"
I'm not judging any one of those people. But let me tell you, I can't put into words how I know there is a God, I just do. I can tell you that there is nothing in His Word that doesn't hold true. I know that history marks Him though it seems we don't teach Him anymore. We even mark our days with His birth (BC - before Christ, AD Anno Domini, the year of the Lord).
Why was my life saved from an eternity in Hell? Grace
Why do I get to love? Grace
How do I know there is a God? Grace
His Grace covers me when I sin. His grace gives me peace when I'm in a room full of people and anxious. His grace allows me to love and not be bitter. His grace allows me to be forgiven. His grace is how I know.
2 Cor 12:9 But he said to me, "My grace is sufficient for you, for my power is made perfect in weakness." Therefore I will boast all the more gladly about my weaknesses, so that Christ's power may rest on me.